Staff at Hatton Country World in Warwickshire couldn't understand why they suddenly had 100 pregnant guinea pigs on their hands - until they released one of the male rodents had managed to escape his enclosure and infiltrate the female-only enclosure.
They noticed that the exhausted father-to-be, now nicknamed Randy, had lost a little weight, but did not realise why until they discovered he was actually a male rodent being kept busy in the wrong pen.
The animal park, which already has 300 male and female guinea pigs, is now readying itself for a population boom in the next few weeks.
Manager Richard Craddock said: "One of our male guinea pigs managed to find his way into the female enclosure and had a very good time by the looks of it.
"We suspect a child may have placed him back in the wrong pen by accident after stroking him or Randy may have somehow broken out of his enclosure to get to the females. "
"We believe that the newly-named Randy could have impregnated up to 100 female guinea pigs, which have litters of about four, so if you do the maths we could be expecting quite a baby boom.
"We don't know how long Randy was in the female enclosure but it could have been several weeks which would have given him time to go round the entire female population.
"Staff did comment he looked a little thinner than before. He has now re-joined his male friends, clearly he's got a lot of bragging to do."
Staff are now looking to build an extension to the guinea pig farm to accommodate Randy's huge brood.